The invention relates to a microprobe system particularly a microprobe system for medical applications especially for stereotactic neurotherapy.
In the medical field as well as in biological research, microprobes are used which are inserted into a tissue where a body structure is to be specifically influenced or scanned. A specific example is the treatment of essential tremor orxe2x80x94in connection with Parkinson""s diseasexe2x80x94of therapy-refracted tremors. To this end, a microelectrode is introduced in the ventral intermediate core (VIM) of the thalamus of a patient in an accurately controlled manner. This microelectrode is then connected to an electrical stimulator, which is implanted subcutaneously below the clavicle. Such a xe2x80x9cbrain pacemakerxe2x80x9d can effectively stop the involuntary action tremor so that the quality of life of the patient is drastically improved.
For other diseases such as Akinese or drug-induced excess movements other targets will be used, i.e. the nucleus subthalamicus or the globus pallidus. Furthermore, brain areas, which are responsible for some disease symptoms, are being coagulated (destroyed) recently with the aid of microelectrodes. This procedure is different for different target areas. It is either pallidotomy (target area globus pallidus) or thalamotomy (target area thalamus).
The location is usually determined with electrophysiological depth recordings of neuronal discharge patterns along a given stereotactic path. The correct determination of a naturally very small target area in the brain is always crucial because a displaced pacemaker electrode would damage, and stimulate, neighboring brain areas, i.e.xe2x80x94fiber sections such as the visual or the pyramid lines.
Conventional recording systems have manual micrometer propulsions, which only permit a relatively inaccurate positioning which is afflicted with errors. Usually, the microelectrode position is only read from a micrometer screw and then manually recorded in an operation protocol. The values may include reading mistakes and inaccuracies. The microelectrode position is not recorded simultaneously with the digitally recorded sensor values. Furthermore, during the electrode forward feeding, the signal recording is susceptible to errors. Due to their dimensions, the recording electrodes are mostly not selective enough to scan individual cells. Therefore, the probability of the signal recording being correct is relatively low. All these circumstances result in a prolonged operations and uncertain success.
Another essential disadvantage of the conventional techniques is the fact that the macro therapy electrode (brain pacemaker) may shift from its position after it has been accurately positioned and part of the stereotactic system (guide tube) is removed. In order to correct any error caused thereby the therapy electrode has to be re-positioned which is quite difficult. A new manual search of the target point determined in advance is necessary with the aid of the described stereotactic measures without the stereotactic aids, which is time consuming and unnecessarily prolongs the operation.
It is an important object of this invention to overcome these and other disadvantages of the state of the art with the most economic means and to create an improved microprobe system that operates with high precision of positioning at a considerably reduced operating time and, at the same time, provides for a documentation permitting a reconstruction of the procedure in order to obtain further information.
In a microprobe system for medical applications particularly for use in neurophysiology and neurosurgery a target determining arrangement is provided which can be mounted on a patients head by means of an adjustable mounting device. An adapter is removably attached to the mounting device and carries a manipulator with a removable probe unit that can be moved by a drive unit which is electrically controllable according to spatial coordinates (x,y,zxe2x80x94respectively, R,xcfx86). The probe unit includes a guide tube for receiving an exchangeable microfiber electrode, which includes sensor areas at its pointed tip for the recording of brain activity signals. They can be stored with a PC-interface in a data acquisition unit, which is in communication with an output unit. The manipulator includes a microfiber electrode control unit, for example, an XYZ-slide with locking means as well as a base body for the attachment of the probe unit to the mounting device in a predetermined orientation.
This new system is distinguished by an exactly controllable, propulsion arrangement, whereby manual uncertainties are avoided. The microfiber electrode delivers neuronal signals during its movement which signals are processed and continuously recorded in the data acquistion unit together with the extremely accurate instant data concerning the microelectrode position. This permits an exceptionally precise error-free guidance of the microprobe into the target area. In contrast to the necessity of prior art arrangements to record the signal and micro-stimulate the tissue in separate processes, one after the other, the system according to the invention integrates these steps with the effect that the operation time is greatly shortened. Since the exact position of the microfiber electrode is digitally recorded and evaluated at any time, all data for the placement of the actual macro therapy electrode are fully available and controllable at any time, either by way of monitor or loudspeaker presentation or by a print-out of a protocol.
Preferably, the manipulator includes a carrier unit for the alignment and guiding of the microfiber electrode and/or the macro therapy electrode along the preferred direction, which preferably includes a guide tube in which the microelectrode and the macro therapy electrode can be inserted alternately. The carrier unit provides always for an identical alignment of the electrodes, which have to be inserted successively so that a certain position established with the microelectrode can be accurately assumed by the macroelectrode.
Of particular advantage is the measure whereby the macrotherapy electrode, in the guide tube can be moved to a predetermined position and at least sections thereof can be uncovered in this position. Such pre-determined position obtained with the aid of the probe unit can be retained very simply and reliably with the guide tube. Moreover, the macroelectrode position in the guide tube can be fixed at the head skin of a patient during an operation without the risk of losing the already adjusted position even though the electrode is subsequently exposed.
For exposing the macroelectrode, the length of the guide tube is variable. Preferably, a telescopic guide tube is used for this purpose and the guide tube can be locked at any extension lengths.
The microfiber electrode may also be integrated in the probe unit so that it can be fixed with the probe unit at the manipulator. Preferably, the probe unit has a microelectrode carrier unit for the pick-up and guiding of the microfiber electrode as well as a microelectrode manipulator for the controlled movement of the microfiber electrode. In this way, an especially accurate and reliable movement of the electrode is obtained. In addition to the electronic processing of the position data, the microelectrode manipulator includes an mechanical-optical position detector for the recording and display of the microelectrode position. As the electronic position detector enables the simultaneous sensing and recording of the position data of the microelectrode with the aid of a PC-supported data acquisition unit and the display of the exact micrometer position of the data gained on a PC-monitor, the mechanical-optical indication of the position permits the direct indication of the travel distance of the microelectrode with an accuracy of 1 mm. Therefore, it serves as a countercheck for the neurosurgeon for the indirect electronic position indication of the microelectrode. Altogether, the documentation of the operation is substantially simplified and is much more precise. Furthermore, the gained data are excellently suitable for a postoperative scientific evaluation.
It is advantageous if the microelectrode carrier unit has a guide tube that can accept a microfiber electrode and can be introduced into the guide tube of the carrier unit when the probe unit is attached to the manipulator. As a result, if a certain position of the probe unit and also the guide tube has been established by an earlier measurement with the microfiber electrode, the guide tube assumes the position required for the introduction of the stimulation electrode without any further adjustment.
In a particular embodiment, the microfiber electrode includes conductors embedded in quartz glass, especially one central conductor surrounded by three symmetrical outer conductors in a slightly spaced relationship. This configuration forms a tetrode with very small dimensions so that the probability of recording in a small space is considerably improved. Presently, only a single channel recording system is available worldwide which is offered by Axon Instruments, Inc. It is called Guideline 3000. It has no motor drive of the microfiber electrode.
Preferably, the outer diameters of the microfiber electrode, the central conductor and the outer conductors have a relation to each other in the area of 6:1, 5:1 to 5:1, 2:1. A high selectivity is obtained mainly with an embodiment in which the microfiber electrode has a pointed tip on which the conductors are exposed so as to form sensor areas. The central conductor forms a cone-shaped tip and the outer conductors form elliptical area. In this way, relatively large sensor areas are obtained with a small electrode diameter, whereby the probability of detecting the neurons is greatly increased.
If the conductor consists of a high strength metal, for example, of a platinum-tungsten alloy (Pt95/W5), the probe has a very high buckling resistance so that it can also be introduced without any problems into layers with high tenacity, i.e. dura.
In order to control the advance of the microelectrode, it is advantageous if the microelectrode manipulator is provided with a microprocessor which can determine the target coordinates (x, y, z respectively, R, xcfx86) for the probe unit utilizing the position and activity data. The output signals provided by the microprocessor may also generate visible and/or audible indications, i.e. an acoustic pattern transmitted by loudspeakers, which may be helpful during the operation. In this way, a surgeon is able to identify a target area on the basis of the neuronal action impulse pattern along the microelectrode travel path.
Besides, the establishment and the use of the recorded data are relatively simple because the output signals of the micro processor are directly supplied to a data storage device. In the data storage device, the data are stored and can be retrieved whenever necessary. This facilitates and accelerates the evaluation considerably.
Further characteristics, details and advantages of the invention will become apparent from the following description of preferred embodiments of the invention on the basis of the drawings: